linux-kernel - Re: [PATCH] m32r: add simple dma

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Date:   Thu, 3 Nov 2016 12:13:18 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:     linux-kernel@...r.kernel.org, fengguang.wu@...el.com
Subject: Re: [PATCH] m32r: add simple dma

On Sun, 30 Oct 2016 23:47:29 +0530 Sudip Mukherjee <sudipm.mukherjee@...il.com> wrote:

> On Friday 21 October 2016 08:59 AM, Andrew Morton wrote:
> > On Sat,  8 Oct 2016 23:23:18 +0530 Sudip Mukherjee <sudipm.mukherjee@...il.com> wrote:
> >
> >> Some builds of m32r were failing as it tried to build few drivers which
> >> needed dma but m32r is not having dma support. Objections were raised
> >> when it was tried to make those drivers depend on HAS_DMA.
> >
> > Huh.  What were these objections?  That sounds like the appropriate
> > fix.  And I suggest that a summary of those objections be captured in
> > this patch's changelog.
> 
> Sorry for the delay in reply. Got busy in dayjob and relocation.
> 
> I was asked to provide dma stubs instead of adding HAS_DMA in the Kconfig.
> 
> http://www.spinics.net/lists/kernel/msg2277152.html
> 
> And an old thread-
> http://www.spinics.net/lists/alsa-devel/msg50931.html
> 
> It appeared to me that instead of adding dma stubs and returning error 
> values from them it will be better to add dma_noop to m32r. Looking at 
> the simplicity of dma_noop it seems that it should work.
> What will you suggest? Do i send v2 after adding the "dma stub" comment 
> and the link to the thread in the commit message or should I opt for dma 
> stub?

Disabling DMA in Kconfig is the most cautious approach.  If someone
cares then they will be able to runtime test the thing, so those people
can implement dma_noop (or something else).

On the other hand, we could just go ahead and wire up dma_noop and if
someone later has problems with it, they will report or fix those
problems.

So, umm, I guess that wiring up dma_noop gets us further forward than
simply disabling everything, so how about we do that?